ADVANTAGES OF KNOWLEDGE OF VEGETABLE PHYSIOLOGY. 185 
lators kept close the atmosphere in the house may be kept at 
the proper temperature, and it will assist vegetation instead of 
destroying it. It should be remembered that in every glass¬ 
house there is always top ventilation through the laps of the 
glass, and, generally speaking, I think a one-foot swing ventilator 
at each end of the house would meet the case, and not give 
the opportunities of abuse which the present system of top 
ventilation does. I am sure that many hybrid Orchids, and 
also many rare species, have departed from this cause alone. 
Once well established, however, the home-raised Orchids 
have a decided advantage over the imported plants, in that they 
are much less liable to be affected by our long spells of dull 
weather and other climatic peculiarities. 
THE ADVANTAGES TO GARDENERS OF SOME 
KNOWLEDGE OF VEGETABLE PHYSIOLOGY. 
By the Rev. Prof. G. Henslow, M.A., F.R.H.S., V.M.H. 
[Substance of a Lecture delivered at the Society’s Gardens, Chiswick, 
June 15, 1898.] 
Inteoduction : What is Vegetable Physiology ? — It is 
the study of the natural history of living plants. 
To secure health in a human being a doctor must understand 
the structure, functions, and requirements of every organ of the 
body ; e.g. the lungs are so made as to absorb oxygen from the air 
for breathing, by which life is kept up ; and one might make a 
somewhat analogous statement of a leaf—that it is so made as 
to absorb carbonic acid gas, by which plant structure is built up. 
Similarly, with regard to the digestive organs, a doctor must 
know the nature of all the organs of secretion, the relative 
values of various foods and how they can best secure the growth 
and development of the body as well as restore its waste. 
Similarly, to understand how a plant may grow well and thrive 
it is necessary to know the structure of its organs or members, 
what they do and what they require. 
Some persons fancy that they can draw a sharp line between 
practice and science, or between cultivation and physiology. 
Such, however, is altogether a mistake ; for all practical 
